Transition State Analogue Structures of Human Phosphoglycerate Kinase Establish the Importance of Charge Balance in Catalysis

Transition state analogue (TSA) complexes formed by phosphoglycerate kinase (PGK) have been used to test the hypothesis that balancing of charge within the transition state dominates enzyme-catalyzed phosphoryl transfer. High-resolution structures of trifluoromagnesate (MgF3 −) and tetrafluoroaluminate (AlF4 −) complexes of PGK have been determined using X-ray crystallography and 19F-based NMR methods, revealing the nature of the catalytically relevant state of this archetypal metabolic kinase. Importantly, the side chain of K219, which coordinates the α-phosphate group in previous ground state structures, is sequestered into coordinating the metal fluoride, thereby creating a charge environment complementary to the transferring phosphoryl group. In line with the dominance of charge balance in transition state organization, the substitution K219A induces a corresponding reduction in charge in the bound aluminum fluoride species, which changes to a trifluoroaluminate (AlF3 0) complex. The AlF3 0 moiety retains the octahedral geometry observed within AlF4 − TSA complexes, which endorses the proposal that some of the widely reported trigonal AlF3 0 complexes of phosphoryl transfer enzymes may have been misassigned and in reality contain MgF3 −.